This disclosure relates to a receiving circuit, a transmission circuit and a system and, more particularly, to a receiving circuit, a transmission circuit and a system which can reduce the effect of noise.
An FSK receiving circuit which demodulates a signal modulated by FSK (Frequency Shift Keying) includes a detector which detects a received signal and a voltage comparison unit which outputs a digital signal based on the voltage of the received signal after detection and a reference voltage.
In Japanese Unexamined Patent Application Publication No. Hei 6(1994)-37822, it is disclosed that: an FSK signal detected by a detector is branched; one of the voltages resulting from branching is inputted to a voltage comparison unit; from the other of the voltages resulting from branching, a dc voltage component is extracted and the extracted dc voltage component is inputted to a reference voltage generation unit; and, at the reference voltage generation unit, a reference voltage is generated from the dc voltage component and the generated reference voltage is inputted to the voltage comparison unit. Also, according to Japanese Unexamined Patent Application Publication No. Hei 6(1994)-37822, the variation of the dc voltage inputted to the voltage comparison unit and the variation of the dc voltage outputted from the reference voltage generation unit become equal, so that the voltage comparison unit can generate, out of the output from the detector, a digital signal with an accurate data bit width.